The invention relates to a process for increasing the conversion of a cracked gasoline feedstock to ethylene and propylene with a low rate of coke formation during the conversion of such hydrocarbons in the presence of an improved zeolite-based catalyst material.
It is known to catalytically crack non-aromatic gasoline boiling range hydrocarbons, particularly hydrocarbons such as paraffins and olefins, to lower olefins (such as ethylene and propylene) and aromatic hydrocarbons (such as benzene, toluene and xylenes) in the presence of catalysts which contain a zeolite (such as ZSM-5), as is described in an article by N. Y. Chen et al. in Industrial & Engineering Chemistry Process Design and Development, Volume 25, 1986, pages 151-155. The reaction products of the catalytic cracking processes contain a multitude of hydrocarbons such as unconverted C.sub.5 + alkanes, lower alkanes (methane, ethane, propane). lower alkenes (ethylene and propylene), C.sub.6 -C.sub.8 aromatic hydrocarbons (benzene, toluene, xylenes and ethylbenzene) and C.sub.9 + aromatic hydrocarbons. It can be desirable to further process the product from a catalytic gasoline cracking operation to increase the yield of compounds that, in a current market, are relatively more valuable than other products of gasoline cracking. The cracking operation yield of lower olefins (such as ethylene and propylene) and BTX (benzene, toluene, xylene and ethylbenzene) aromatics, for example, can be increased using the improved zeolite catalyst compositions of this invention.
In the conversion of hydrocarbons to aromatic hydrocarbons and lower olefins using zeolite catalysts an excessive amount of coke can be formed. The formation of coke during the zeolite catalyzed aromatization of hydrocarbons tends to cause catalyst deactivation. In processes for the aromatization of hydrocarbons and the formation of lower olefins from hydrocarbons it is, therefore, desirable to minimize the formation of coke.